Trish & Tammy'sN0USR.Com

Portable and Emergency Power Considerations for the KX3

Beginning a discussion of the Elecraft KX3's power consumption
and requirements for portable and emergency power use let's start out by
quoting Elecraft's specifications as listed in the manual for reference.
For the sake of all of my discussions please assume the unit requires a
negative ground and the stock microphone is used. Also installed
in this KX3 are the KXBC3 realtime clock/internal charger, the KXAT3
auto tuner, and the KXFL3 filter. If you are using this discussion
to compare the KX3 to the FT-817ND Please remember to keep it fair. The
KX3 can output a max of 10 watts and the FT-817ND 5 watts.

The antenna was connected to a dummy load.
Non-squelched volume level set to 50% on internal speaker. We
chose 3.97Mhz as our test frequency as we most often operate voice in
that area. We chose Data as the operating mode to represent
maximum modulation.

The test results show the rig as a good choice for
those wanting the full features of a modern style rig. The KX3's
current draw comes in less on our 80m tests than our Yaesu FT-817ND
however we were surprised to find the FT-817ND as the winner for low
current draw on 6m!

Internal Batteries
Since we have the internal charging unit we stock out KX3 with name
brand AA NiMH 2650mAh cells. We find our KX3 draws ~ 340mA while
charging the internal cells. We typically let the KX3 charge the
cells and select a charging time based on how depleted the the batteries
are at the time. Since the KX3 doesn't seem to have a way of
sensing the batteries charge level we will every so many months remove
the cells and run them thru a discharge/charge conditioning cycle on an
external charger.

External PowerLike the the FT-817 is much more flexible when it comes to external power
sources as can run on anything from 8 to 15VDC as long as it can supply
a minimum of 500mA current (Note: With a 500mA external
source you should be able to use the internal charger to charge your
internal batteries and listen to your hearts content however to transmit
with such a supply you would need to limit your transmit power to 200mW
or less.

Our KX3 and 817 follow us around most of the time
running off of one of our 13.4v LiFePO4 battery packs which we charge
with a pair of 28w of solar panels, by the time one is run down (about two days
of monitoring with about 30 min talk time per day) the next has been
recharged (even on cloudy days). We also have a 300w solar
panel array residing on our roof which is connected full time to our ham
shack and base equipment. A single 10w portable cell is enough to run
the radio in receive mode but does not supply enough current for
transmit but it does a nice job of trickle charging the internal
batteries batteries. The 10w panel supplies about 560mA in full
sun. The 300w array on our roof can supply ~18A and is enough to run
our entire station, even in full 100w transmit mode (Note: We use a solar
charge controller to limit the arrays voltage, without the controller
the array can supply as much as 21VDC under low/no load conditions which would most
likely fry our favorite radios.)